1 GEOTHERMAL SYSTEMS AND TECHNOLOGIES 8. ENVIRONMENTAL EFFECTS OF GEOTHERMAL ENERGY
8. ENVIRONMENTAL EFFECTS OF GEOTHERMAL ENERGY 2 Geothermal resources are considered renewable and “green”, however, there are several environmental impacts that must be considered during utilization. These are: be considered during utilization. These are: � emission of harmful gases, � noise pollution, � water use and quality, � land use, and � impact on natural phenomena, wildlife and vegetation.
8.1. Emissions 3 The potential gases that can be released, are: � carbon dioxide, � sulfur dioxide, � nitrous oxides, � nitrous oxides, � hydrogen sulfide along with particulate matter Gaseous emissions For hydrothermal installations, the most common NCGs are CO 2 and H 2 S, although species such as: methane, hydrogen, sulfur dioxide, and ammonia are often encountered in low concentrations.
Carbon dioxide (CO 2 ) 4 Geothermal plants emit CO 2 , but in small quantities when compared to fossil fuel-fired emissions. Amounts of CO 2 in geothermal fluids can vary depending on location, and Amounts of CO 2 in geothermal fluids can vary depending on location, and the amount of CO 2 actually released into the atmosphere can vary depending on power plant design. NCGs such as CO 2 make up less than 5% by weight of the steam phase of most geothermal systems. Of that 5%, CO 2 typically accounts for 75% or more of non-condensable gas by volume.
Nitrogen oxides (NOx) 5 Geothermal power plants emit very low levels of NOx. In most cases, geothermal facilities emit no nitrogen oxides at all. In most cases, geothermal facilities emit no nitrogen oxides at all. The small amounts of NOx released result from the combustion of hydrogen sulfide (H 2 S). Geothermal facilities are generally required by law to maintain H 2 S abatement systems that capture these emissions, and either burn the gas or convert it to elemental sulfur.
Hydrogen sulfide (H 2 O) 6 Today, geothermal steam and flash power plants produce only minimal H 2 S emissions. Binary geothermal power plants release no H 2 S emissions at all. Binary geothermal power plants release no H 2 S emissions at all. Sulfur dioxide (SO 2 ) Geothermal power plants do not emit SO 2 directly. Once H 2 S released, it spreads into the air and eventually changes into SO 2 and sulfuric acid.
Particulate Matter 7 Particulate matter (PM) is a broad term for a range of substances that exist as discrete particles. PM includes liquid droplets or particles from smoke, dust, or fly ash. While coal- and oil-fired power plants produce hundreds of tons of PM annually, While coal- and oil-fired power plants produce hundreds of tons of PM annually, geothermal power plants emit almost none. Water-cooled geothermal power plants give off small amounts of PM from cooling towers when steam condensate is evaporated, but the amount is quite small when compared to coal- or oil-fired power plants.
Mercury 8 If mercury is present in a GR, using that resource for power generation could result in mercury emissions, depending upon the technology used. The binary power plants do not emit mercury. Ammonia (NH 3 ) Geothermal accounts for only a fraction of ammonia emissions, at substantially lower quantities than one percent. Emitted ammonia can combine with water to form NH 4 OH.
Boron 9 In geothermal steam systems, boron is present in the steam as highly soluble boric acid. When combined with ammonia, it often forms white crystalline When combined with ammonia, it often forms white crystalline salt deposits on equipment exposed to geothermal steam. New geothermal plants are now required to install high efficiency drift eliminators for particulate control regardless of boron content in the water, and these eliminators reduce boron emissions.
8.2. Solid and liquid waste 10 Arsenic Geothermal plants are not considered to be high arsenic emitters even though arsenic is common to volcanic systems. arsenic is common to volcanic systems. When arsenic is present in a geothermal system, it typically ends up in the solid form in the sludge. Silica and Other Waste Products Concentrations of silica are low enough in geothermal facilities that workers are not at risk.
8.3. Noise 11 The majority of the noise produced at a power plant or direct-use site is during the well drilling operation, which normally shuts down at night. The noise from a power plant is extremely low. Most of the noise comes from cooling fans and the rotating turbines. Noise pollution from geothermal plants is typically considered during three phases: Noise pollution from geothermal plants is typically considered during three phases: � the well-drilling and testing phase, � the construction phase, and � the plant operation phase. Noise from normal power plant operation generally comes from the three components of the power plant: � the cooling tower, � the transformer, and � the turbine-generator building.
Sound Level Noise Source (dBA) Geothermal normal operation 15 - 28 8.3. Noise Near leaves rustling from breeze 25 12 Whisper at 1,8 m 35 Inside average suburban residence 40 Near a refrigerator 40 Geothermal construction 51 - 54 Geothermal well drilling 54 Inside average office, without 55 Common Sound Levels nearby telephone ringing Speech at 0,9 m, normal voice level 60 Auto (96 km per hour) at 30,5 m 65 Vacuum cleaner at 3 m 70 Garbage disposal at 0,9 m 80 Electric lawn mower at 0,9 m 85 Food blender at 0,9 m 90 Auto horn at 3 m 100
8.4. Water quality and use 13 Water use in EGS projects: Well drilling, reservoir stimulation and circulation. • Fluids produced from the reservoir. • Cooling water for heat rejection. Cooling water for heat rejection. • • Geothermal plants use about 20 liters/MWh, while binary air-cooled plants use no fresh water. The geothermal fluids contain varying concentrations of potentially toxic minerals and other elements and are extremely hot when they reach the surface of the Earth. For these reasons, geothermal waters can be dangerous to humans and surrounding ecosystems.
8.5. Land use 14 Geothermal power plants are designed to “blend- in” with the surrounding landscape. Typically, a geothermal facility uses 404 m 2 of land per GWh. per GWh. Geothermal uses less land than many other sources. Geothermal power plants impose minimal visual impacts on their surroundings when compared to typical fossil-fuel plants. Typical pipeline at Miravalles GPP, Costa Rica (photo by R. DiPippo)
Subsidence 15 Subsidence is most commonly thought of as the slow, downward sinking of the land the slow, downward sinking of the land surface. Although it can occur naturally, subsidence can also occur as a result of the extraction of subsurface fluids, including groundwater, hydrocarbons, and geothermal fluids. Sink Hole Caused by Geothermal Drilling
Induced seismicity 16 Although it typically occurs naturally, seismicity has at times been induced by human activity, including the development of geothermal fields, through both production and injection operations. operations. In these cases, the resulting seismicity has been low-magnitude events known as “micro earthquakes”. The micro earthquakes sometimes associated with geothermal development are not considered to be a hazard to the geothermal power plants.
Landslides 17 The extent to which geothermal development induces landslides is unclear, as landslides, which occur naturally in certain areas of geothermal activity such as volcanic zones, are produced by a combination of events or circumstances rather than by any single combination of events or circumstances rather than by any single specific action.
8.6. Impact to wildlife and vegetation 18 Plants are usually prevented from being located near geysers, fumaroles and hot springs. Most plants are located in areas with no Most plants are located in areas with no natural surface discharges. Any site considered for a GPP, must be reviewed and considered for the impact on wild-life and vegetation, and if significant, provide a mitigation plan. Imperial Valley Power Plant and Productive Farmland
8.6. Impact to wildlife and vegetation 19 Direct use projects are usually small and thus have no significant impact on natural features. Geothermal plants are designed to minimize the potential effect upon wildlife and vegetation: vegetation: � pipes are insulated to prevent thermal losses, � power plants are fenced in so as to prevent wildlife access, � spill containment systems with potential to hold 150% of the potential maximum spill are put in place, and � areas with high concentrations of wildlife or vegetation specific to an area are avoided.
8.7. Thermal pollution 20 Heat rejection from geothermal plants is higher per unit of electricity production than for fossil electricity production than for fossil fuel plants or nuclear plants; because the temperature of the geothermal stream that supplies the input thermal energy is much lower for geothermal power plants.
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